1. Field of the Invention
This invention relates to a propellant composition made from a lacquer and processed to form hollow propellant grains that are useful for ammunition rounds. More particularly, the invention is directed to a low viscosity lacquer that is continuously processed by extrusion to form hollow hardened propellant grains in a liquid slurry.
2. Description of Related Art
Perforated propellant grains are generally produced by extruding lacquers having between 0 and 20% by weight of solvent. This method of production requires a pressure in the range of between about 1000 and 5000 psi to extrude the lacquer through an extrusion die assembly, and requires large quantities of energy and expensive equipment. The following U.S. Patents are representative of the state of the art.
U.S. Pat. No. 5,821,449 entitled, xe2x80x9cPropellant grain geometry for controlling ullage and increasing flame permeabilityxe2x80x9d that issued on Oct. 13, 1998 discloses hollow grain propellants for use in lightweight training rounds.
U.S. Pat. No. 4,841,863 entitled, xe2x80x9cSaboted, light armour penetrator round with improved powder mixxe2x80x9d that issued on Jun. 27, 1989 discloses propellant in the form of spheroidal (substantially spherical) powders and recites that a batch process for the manufacture of spherical powders is disclosed in U.S. Pat. No. 2,027,114 and a continuous process in U.S. Pat. No. 3,679,782.
U.S. Pat. No. 5,524,544 entitled, xe2x80x9cNitrocellulose propellant containing a cellulosic burn rate modifierxe2x80x9d that issued on Jun. 11, 1996 and U.S. Pat. No. 5,510,062 entitled, xe2x80x9cMethod of producing a nitrocellulose propellant containing a cellulosic burn rate modifier infiltrated therein that issued on Apr. 23, 1996 disclose a solvent process for the manufacture of propellant grains where a burn rate deterrent is gradationally dispersed within the propellant with the greatest concentration of deterrent at the particulate periphery.
U.S. Pat. Nos. 2,027,114; 3,679,782; 4,841,863; 5,510,062; 5,524,544 and 5,821,449 are all incorporated by reference in their entireties herein.
Accordingly, what is needed in the art is a lacquer composition and method of manufacturing that efficiently produces perforated propellant grains in a safe and economical manner, and at a lower extrusion pressure than presently used. The present invention is believed to be an answer to that need.
In one aspect, the present invention is directed to a propellant composition made from a lacquer, the lacquer comprising: (a) from about 15 to about 70 wt % of an organic solvent; (b) from about 0.1 to about 2.5 wt % of a stabilizer; (c) optionally, from about 0% to about 40 wt % of an energetic plasticizer; (d) optionally, from about 0 to about 10 wt % of a nonenergetic plasticizer; (e) optionally, from about 0 to about 10 wt % water; (f) optionally, from about 0 to about 15 wt % of additional additives; and balance being nitrocellulose; all weight percents based on the total weight of the composition, and wherein the lacquer has a viscosity of less than 10 million centipoise when processed.
In another aspect, the present invention is directed to a propellant composition made from a lacquer, the lacquer consisting essentially of: (a) from about 30 to about 65 wt % of an organic solvent selected from the group consisting of ethyl acetate, ether, acetone, and combinations thereof; (b) from about 0.25 to about 1.5 wt % of a stabilizer selected from the group consisting of diphenylamine, ethyl centralite, diethyldiphenylurea, 2-nitrodiphenylamine, N-nitrosodiphenylamine, and combinations thereof; (c) optionally, from about 5% to about 25 wt % of nitroglycerin as an energetic plasticizer; (d) optionally, from about 0 to about 3 wt % of a nonenergetic plasticizer selected from the group consisting of dibutylphthlate, adipate esters, and combinations thereof; (e) optionally, from about from about 0 to about 4 wt % water; (f) optionally, from about 0 to about 15 wt % of additional additives selected from the group consisting of lubricants; coolants; barrel wear additives; flash suppressants; decoppering agents; energetic solids, and combinations thereof; and balance being nitrocellulose; wherein all weight percents are based on the total weight of the composition, and wherein the lacquer has a viscosity of between 1 million and 3 million centipoise.
In another aspect, the present invention is directed to a method for manufacturing perforated propellant grains, comprising the steps of: extruding a propellant lacquer through an extrusion die assembly to form one or more propellant lacquer strands, the extrusion die assembly having a plurality of holes, each of the holes having at least one pin tip positioned therein, the propellant lacquer comprising: (a) from about 15 to about 70 wt % of an organic solvent; (b) from about 0.1 to about 2.5 wt % of a stabilizer; (c) optionally, from about 0% to about 40 wt % of an energetic plasticizer; (d) optionally, from about 0 to about 10 wt % of a nonenergetic plasticizer; (e) optionally, from about 0 to about 10 wt % water; (f) optionally, from about 0 to about 15 wt % of additional additives; and balance being nitrocellulose; all weight percents based on the total weight of the composition, and wherein the lacquer has an extrusion viscosity of less than 10 million centipoise; cutting the propellant lacquer strand to a desired dimension to form perforated propellant grains; suspending the perforated propellant grains in a water based liquor; removing the organic solvent and water from the perforated propellant grains; and hardening the perforated propellant grains.
In another aspect, the present invention is directed to a propellant grain having outwardly extending ridges.
In another aspect, the present invention is directed to a propellant grain having an ellipsoidal cross section.
These and other aspects will be more fully understood from the following detailed description of the invention.